What's the "een" in Halloween?
1650s, "cooperation," from Modern Latin synergia, from Greek synergia "joint work, assistance, help," from synergos "working together," related to synergein "work together, help another in work," from syn- "together" (see syn-) + ergon "work" (see urge (v.)). Meaning "combined activities of a group" is from 1847.
synergy syn·er·gy (sĭn'ər-jē)
The interaction of two or more agents or forces so that their combined effect is greater than the sum of their individual effects.